Closure is a key concept in many programming languages ​​like Swift. They provide a way to define activity and encode it into a self-contained set of rules. Closures in Swift are frequently in comparison to capabilities, however they’re less difficult and greater concise in their syntax.

Closure in swift

What about closures?

The comparison is a self-contained rule that can be:

  • Stored in a variable or constant.
  • Passed as an argument to functions.
  • Returned from functions as a value.

Closure retrieves and stores references to variables and constants in internally defined contexts. This lets in those values ​​to be accessed and acted upon even though they’re no longer complete.

Closure syntax

The Closure syntax in Swift is compact and simple. Here is the basic structure of Closure:

let closureName: (parameters) -> ReturnType = { (parameters) -> ReturnType in
    // Closure body
    // Code to be executed when the closure is called
    return returnValue
  • ClosureName: This is an optional variable or constant name that can be used to refer to the closure.
  • (parameter) -> ReturnType: This is the closure type annotation, which specifies the form of parameters it takes and the go back type it gives.
  • (parameters) -> go back kind in … : This is the frame of the closure, enclosed within curly braces. It carries the code to be achieved while the closure is known as. These key phrases separate parameter and go back type declarations from the frame.

Closure Example

let addClosure: (Int, Int) -> Int = { (a, b) -> Int in
    return a + b

let result = addClosure(3, 5) // result is 8

In this example, addClosure is a closure that takes two integers as parameters and returns their sum.

Shorthand Syntax

Swift provides shorthand argument names for closures, making them more concise. For example, you can use $0$1$2, and so on to refer to the first, second, third, and subsequent parameters of the closure.

Here’s the same addClosure example using shorthand argument names:

let addClosure = { $0 + $1 }
let result = addClosure(3, 5) // result is 8

Use Cases for Closures

Closures are utilized in various scenarios in Swift, such as:

  • Sorting collections.
  • Performing asynchronous operations.
  • Defining custom operations for functions like map, filter, and reduce.
  • Encapsulating capability to be performed later.

Closures are a powerful tool for creating reusable, modular, and expressive code in Swift. They are essential for understanding many aspects of Swift programming, and mastering closures is a key step in becoming proficient in the language.

// Define a closure that takes an array of integers and returns a new array with each element squared
let squareClosure: ([Int]) -> [Int] = { numbers in
    var squaredNumbers = [Int]()
    for number in numbers {
        squaredNumbers.append(number * number)
    return squaredNumbers

// Call the closure
let numbers = [1, 2, 3, 4, 5]
let squaredNumbers = squareClosure(numbers) // squaredNumbers is [1, 4, 9, 16, 25]

Closures Examples

1. Sorting with Closures:

Closures are often used to outline custom sorting logic for collections. You can pass a closure to the sorted(by:) method to sort an array according to your criteria.

let numbers = [5, 2, 8, 1, 9, 3]

let sortedNumbers = numbers.sorted { (a, b) -> Bool in
    return a < b
// sortedNumbers is [1, 2, 3, 5, 8, 9]

In this example, the closure specifies that the array should be sorted in ascending order.

2. Filtering with Closures:

You can use closures to filter elements in an array based on a condition.

let numbers = [1, 2, 3, 4, 5, 6, 7]

let evenNumbers = numbers.filter { (number) -> Bool in
    return number % 2 == 0
// evenNumbers is [2, 4, 6]

Here, the closure filters out only the even numbers from the array.

3. Mapping with Closures:

Closures can be used to transform elements in an array using a specified operation.

let numbers = [1, 2, 3, 4, 5]

let squaredNumbers = { (number) -> Int in
    return number * number
// squaredNumbers is [1, 4, 9, 16, 25]

The closure takes each element from the numbers array and squares it, resulting in a new array.

4. Escaping Closures:

Closures can be marked as “escaping” when they’re passed as arguments to a function and might be called after the function returns. This is common in asynchronous programming.

func performAsyncTask(completion: @escaping () -> Void) {
    // Simulate an asynchronous task {
        // Do some work

performAsyncTask {
    print("Async task completed")

In this example, the closure is marked as escaping and is called when the asynchronous task is completed.

5. Trailing Closures:

Trailing closures are a Swift feature that allows you to place a closure argument outside the parentheses when calling a function.

func performOperation(_ operation: () -> Void) {
    // Perform the operation

performOperation {
    print("This is a trailing closure")

It can improve code readability, especially when working with functions that take closures as their last argument.

These examples illustrate the versatility and usability of closures in Swift, from sorting and filtering arrays to handling asynchronous tasks and enhancing code clarity. closures is a effective language function that allows you to jot down concise and expressive code.

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